Comment 1 for bug 1938920

> - Deprecate gateway4 & gateway6 in favor of defaults routes (LP: #1756590)

I'm not sure this is acceptable to land in a stable release. By all means provide a new and cleaner mechanism, and change the documentation to advise the newer method. However, actually printing a deprecation notice on Focal when it was previously the documented way of doing things on Focal, and thus alarming existing users, seems like really poor UX to me for users who expect stability during the lifetime of an LTS. I think such a deprecation notice should only be presented to users after they upgrade to a newer release, which in practice means that you can only introduce deprecation on the Ubuntu development release.

Our remit to make feature changes in stable releases comes with the limitation that they "must not change behaviour on existing installation". I think that this implies that you cannot deprecate behaviour, or print notices about deprecation, either.

What about Hirsute? https://wiki.ubuntu.com/StableReleaseUpdates#Other_safe_cases says that "any such feature must then also be added to any newer supported Ubuntu release". When adding new features, this is a hard requirement. We can't have version numbers "go backwards" as users upgrade through Ubuntu releases.